compression test 85 psi
02-13-04, 06:49 PM
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compression test 85 psi
I heard from mazda that the minimum compression spec of 6 kg/cm^2, which equals 85 psi is that true? So to say that 85 psi on all three faces is bad?
02-13-04, 09:10 PM
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compression #'s
Just for a reference, my brother just bought a '93 FD , with 26K miles and all the compression numbers were like 130psi. ( he's a lucky bastard for gettting that car for only $16,300.)
02-14-04, 02:20 AM
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130 psi = 8.84:1
6:1 compression = 88.20 psi
stock FD rotors are 8.5:1 right? So that would be 124.95 psi.
Of course most compression testers aren't accurate to the .01.....but just to keep things accurate
6:1 compression = 88.20 psi
stock FD rotors are 8.5:1 right? So that would be 124.95 psi.
Of course most compression testers aren't accurate to the .01.....but just to keep things accurate
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02-14-04, 09:39 AM
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Originally posted by suganuma
130 psi = 8.84:1
6:1 compression = 88.20 psi
stock FD rotors are 8.5:1 right? So that would be 124.95 psi.
Of course most compression testers aren't accurate to the .01.....but just to keep things accurate
130 psi = 8.84:1
6:1 compression = 88.20 psi
stock FD rotors are 8.5:1 right? So that would be 124.95 psi.
Of course most compression testers aren't accurate to the .01.....but just to keep things accurate
02-14-04, 12:04 PM
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Stock FD rotors are 9.0:1. Nominal (new) compression is 120psi, minimum is 85psi. Although compression ratio is related to your absolute compression readings, they are not equivalent. That is to say, if atmospheric is 14.7psi and you have a 9.0:1 compression ratio, you will not achieve 9x14.7psi = 132psi on your compression meter. That is simply the maximum possible static compression. Since the test is dynamic compression, plus in the real world no engine seals perfectly, you are always going to see something lower than that. Another interesting thing to note is testing the car cold will result in higher numbers than testing it hot (this has been demonstrated by a list member and was also what Mazdatrix told me). Testing hot is the proper procedure.
02-14-04, 12:52 PM
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Originally posted by Nathan Kwok
Stock FD rotors are 9.0:1. Nominal (new) compression is 120psi, minimum is 85psi. Although compression ratio is related to your absolute compression readings, they are not equivalent. That is to say, if atmospheric is 14.7psi and you have a 9.0:1 compression ratio, you will not achieve 9x14.7psi = 132psi on your compression meter. That is simply the maximum possible static compression. Since the test is dynamic compression, plus in the real world no engine seals perfectly, you are always going to see something lower than that. Another interesting thing to note is testing the car cold will result in higher numbers than testing it hot (this has been demonstrated by a list member and was also what Mazdatrix told me). Testing hot is the proper procedure.
Stock FD rotors are 9.0:1. Nominal (new) compression is 120psi, minimum is 85psi. Although compression ratio is related to your absolute compression readings, they are not equivalent. That is to say, if atmospheric is 14.7psi and you have a 9.0:1 compression ratio, you will not achieve 9x14.7psi = 132psi on your compression meter. That is simply the maximum possible static compression. Since the test is dynamic compression, plus in the real world no engine seals perfectly, you are always going to see something lower than that. Another interesting thing to note is testing the car cold will result in higher numbers than testing it hot (this has been demonstrated by a list member and was also what Mazdatrix told me). Testing hot is the proper procedure.
So fully warmed up 85-120 psi is within spec. What is acceptable as far as difference in compression from face to face? 10psi? 20psi?
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